When air is compressed for use in pneumatic systems and the like, the temperature of the air is raised significantly in the compressor. For example, the outlet air temperature from the compressor may be as high as 350 degrees F. Air at this temperature tends to contain a significant amount of moisture. It is conventional practice to provide some form of moisture removal equipment in the exit stream from the compressor to remove the excess moisture prior to the use of the compressed air. This is particularly essential when the compressed air is used for machine tool air motors, for painting or for other similar applications where moisture would be detrimental.
Several forms of air dryers are known in the art. Probably the most commonly used equipment for the drying involves some piece of equipment which cools the air and then causes the moisture to condense on a surface such that it can be removed to provide air for the pneumatic systems having substantially reduced moisture content.
Numerous refrigerant-type dryers are known in the art. Typical of these dryers are described in U.S. Pat. No. 3,359,753, issued to M. Fiedler, et al, on Dec. 26, 1967; U.S. Pat. No. 4,193,443, issued to K. Nanaumi, et al, on Mar. 18, 1980; U.S. Pat. No. 4,235,081, issued to R. 0. Dowling on Nov. 27, 1980; and U.S. Pat. No. 4,638,852 issued to S. K. Basseen and R. A. Harlan, this patent having a common assignee with the present invention. The latter two patents have the dryer separated into an air-to-air exchanger and an air-to-refrigerant exchanger. The refrigerant-type dryers typically reduce the pressure dew point (PDP) of the pneumatic system air to about 35 to 40 degrees F.
Another general type of dryer is a desiccant dryer wherein moisture is adsorbed on a packing within the dryer. Periodically the collected water is removed (purged) from the packing to maintain the efficiency of the dryer. Usually two such dryer units (towers) are utilized so that as one is being used for drying, the other is being purged. The purging of these desiccant dryers is typically accomplished by one of two techniques. According to one technique, heaters are provided such that the packing can be heated to a temperature sufficient to drive off substantially all of the water to the atmosphere. The heaters can be either internal or external to the dryers. This is a costly construction, and can cause difficulty (e.g. fires) because of the required temperature. The second technique involves passing a portion of the product air through the packing such that this absorbs the moisture so that the disposal of the air to the atmosphere removes the moisture. This technique, when applied to the dryer, gives the dryer the term "heatless" in contrast to the former "heated" dryer. Although less costly to construct, the heatless dryers utilize approximately fifteen percent (15%) of the product air during a purge operation. This of course, requires a pump of greater capacity than when there is no purge loss. These desiccant dryers can provide exit air at a pressure dew point of about -40 degrees F.
Certain patents were located in a preliminary patent search relative to the present invention. These are: U.S. Pat. No. 3,739,594, issued to C. E. Freese on June 19, 1973; U.S. Pat. No. 4,062,129, issued to T. Yoshida, et al. on Dec. 13, 1977; U.S. Pat. No. 4,171,624, issued to G. Meckler, et al. on Oct. 23, 1979; U.S. Pat. No. 4,180,985, issued to L. L. Northrup, Jr. on Jan. 1, 1980; and U.S. Pat. No. 4,259,849, issued to W. C. Griffiths on April 7, 1981.
In addition to the above-identified shortcomings of the dryers of the known prior art, when the dryer used in a pneumatic air drying system fails, the pneumatic system is shut down.
Accordingly, it is a principal object of the present invention to provide a high efficiency drying system to dry air and other gases utilizing a heatless desiccant (or other sorbant) drying medium wherein loss of product air used for purging is substantially reduced.
It is another object of the present invention to provide a high efficiency drying system to dry air and other gases that achieves a pressure dew point of about -40 degrees F. to -100 degrees F. at a minimum cost.
It is also an object of the present invention to provide a high efficiency drying system to dry air and other gases that utilizes separable components such that air/gas can be processed by one component in the event of failure of the second component.
These and other objects of the present invention will become more apparent upon a consideration of a full description of the invention in conjunction with the accompanying drawings.